Observational Evidence for the Origin of High-energy Neutrinos in Parsec-scale Nuclei of Radio-bright Active Galaxies

Abstract

Observational information on high-energy astrophysical neutrinos is being continuously collected by the IceCube observatory. However, the sources of the neutrinos are still unknown. In this study, we use radio very long baseline interferometry (VLBI) data for a complete VLBI flux density–limited sample of active galactic nuclei (AGNs). We address the problem of the origin of astrophysical neutrinos with energies above 200 TeV in a statistical manner. It is found that AGNs positionally associated with IceCube events have typically stronger parsec-scale cores than the rest of the sample. The posttrial probability of a chance coincidence is 0.2%. We select the four strongest AGNs as highly probable associations: 3C 279, NRAO 530, PKS 1741−038, and OR 103. Moreover, we find an increase of radio emission at frequencies above 10 GHz around neutrino arrival times for several other VLBI-selected AGNs on the basis of RATAN-600 monitoring. The most pronounced example of such behavior is PKS 1502+106. We conclude that AGNs with bright Doppler-boosted jets constitute an important population of neutrino sources. High-energy neutrinos are produced in their central parsec-scale regions, probably in proton–photon interactions at or around the accretion disk. Radio-bright AGNs that are likely associated with neutrinos have very diverse γ-ray properties, suggesting that γ-rays and neutrinos may be produced in different regions of AGNs and not directly related. A small viewing angle of the jet–disk axis is, however, required to detect either of them.

Association of IceCube neutrinos with radio sources observed at Owens Valley and Metsähovi Radio Observatories

“…There is also some level of uncertainty in the detector systematic uncertainties and therefore in the reconstruction errors, which is why we use the published upper limit of 1.0 • (IceCube Collaboration 2013) in our analysis. However, following Plavin et al (2020a), we estimate the optimal systematic uncertainty using our data (see Sect. 3).…”

“…Kadler et al (2016) discovered PKS B1424−418 flaring in the radio and γ-ray bands in temporal and positional coincidence with the IceCube neutrino IC35, but this neutrino event had a large positional error circle of 15.6 • . The first systematic search of radio sources was performed only recently, by Plavin et al (2020a), who investigated the association of neutrinos with radio bright AGNs using the VLBI based radio fundamental catalogue (RFC) 1 and RATAN-600 (Korolkov & Pariiskii 1979) data. They found that AGNs positionally associated with high-energy IceCube events typically have stronger parsec-scale cores compared to the rest of the sample.…”

“…Moreover, 1 http://astrogeo.org/vlbi/solutions/rfc_2019c/ they found an average increase of radio emission at frequencies above 10 GHz around neutrino arrival times for several AGNs on the basis of RATAN-600 monitoring. In Plavin et al (2020b) they further analyzed the IceCube point source likelihood map, including also lower energy events, against the RFC catalogue and found a 3σ significance for the correlation between them.…”

Acceleration of the high‐energy protons in an active galactic nuclei

“…Although acceleration is carried out equally for both protons and electrons, due to the more intense synchrotron radiation, the electrons lose a significant energy, which prevents them from reaching maximum energy. According to IceCube results (Plavin 2020), the neutrino energy in the sub-parsec region at the base of the jet corresponds to the energy of colliding protons E p ≃ 10 16 − 10 17 eV, which corresponds to orders of magnitude energy acquired by protons in the region of the SMBH magnetosphere. The simulation uses a kinetic approach to describe the motion of a particle.…”

Baikal-GVD: status and first results

“…The recent point source search with 10 year data of IceCube track-like events indicate 3.3 inconsistency with background for the full Nothern Hemisphere source catalog [6]. Moreover recent studies indicate 4.1 association of IceCube track-like events with radio-bright blazars selected on the basis of very long baseline interferometry observations [7].…”